Method of aligning the upper and lower centering bells of a lens doublet assembly machine

ABSTRACT

A method for aligning the upper and lower centering bells of a lens doublet assembly machine is provided. In one example of the method, the method includes positioning an alignment tool with respect to a base plate of the lens doublet aligning apparatus; positioning an upper bell shaft with respect to the alignment tool, wherein the upper bell shaft includes an upper bell chuck at a lower end of the upper bell shaft; and tightening flexural bearings around an outer radial edge of the upper bell shaft, wherein the flexural bearings precisely hold the upper bell shaft into perpendicular alignment in the lens doublet aligning apparatus.

RELATED APPLICATIONS

This Patent Application claims priority under 35 U.S.C. 119(e) of theco-pending U.S. Provisional Pat. App. No. 60/703,531, filed Jul. 29,2005, entitled “Method for Aligning the Upper and Lower Centering Bellsof a Lens Doublet Assembly Machine”, which is hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to lens doublets for cameras. Moreparticularly, the present invention relates to techniques and machinesfor aligning lens doublets for cameras.

BACKGROUND OF THE INVENTION

Correctional Lens Doublets consist of two lenses generally made ofdifferent optical materials attached to each other to derive betteroptical performance over wavelengths of interest. Currently, the mostpopular methods of achieving micron level centration of the two piecesof lens doublets involve active alignment or other methods.Unfortunately, these methods are slow, high in cost and not amenable tovolume production. The problem of centration is even more difficult forvery small lens pieces such as used in handheld cameras or cell phonecameras.

Active alignment involves passing an optical beam through the lenses orlens assemblies. Controlled movement of the lenses is executed using thelocation of the projected beam image for feedback. The Laser Alignmentand Assembly Station™ of Opto-Alignment Technology, Inc. is an exampleof a apparatus that utilizes active alignment. A rotating air bearingstage has X-Y-theta-phi adjustments to set the lens barrel or otheroptic holder to run true to serve as a reference. Then a reflection froma laser imaged on a CCD camera is used to center multiple opticalelements.

There are several ways in which the lens can be centered on thebell-shaped centering bell. Many of these methods are discussed withfigures in “Fabrication Methods for Precision Optics,” by Hank H. Karow.Brief descriptions are provided here.

An older transfer spindle method is still used for prototype andlow-volume production and for centering lenses made from soft andsensitive materials. According to Karow, the lens is mounted on aprecise centering bell which is fastened on a thread to a precisionspindle. This centering bell is nearly always made of brass, althoughsteel bells are sometimes used as well. The lens is mechanically oroptically aligned on the centering bell so that the optical andmechanical axes of the lens are coincident. The spindle with thecentered lens is then mounted in a centering machine, which is used togrind the diameter of the lens concentric to the axis of rotation.

In one centering method, the lens and the centering bell are heatedsufficiently so that a small amount of a specially formulated centeringwax can be applied to the edge of the centering bell. The heated lens isthen positioned on the centering bell by mechanical means or by anoptical alignment method. For the mechanical method, the edge thicknessvariations must be nulled out or at least reduced to a minimum while thelens rotates. The run-out is monitored by means of a digital indicator.

Another centering method is an optical method that relies on lightreflected off the outer surface of the lens. The lens is mounted on acentering bell, which rotates the lens. The centering bell is mounted tothe spindle.

Yet another centering method is an optical method that relies on therotation of a target image that is projected through the lens. A lamp, acollimating lens and mirrors form the target image and project thetarget image through the lens. The lens is mounted on the centeringbell, which rotates the lens.

A laser beam alignment method is used for more critical centrationrequirements. It is quite similar to the target image projection method.Both of these optical centration methods are only useful for lenses madefrom visually transparent materials. Projection methods are not possiblefor infrared materials and metal optics because they are not transparentin the visible region of the spectrum.

Another centering method is bell chuck centering for small lenses. Usingtwo coaxial bell chucks to align a single lens to the chuck axis. Thelens is typically arranged horizontally. Bell chuck centering is amethod in which a suitably curved lens is self-centering when clampedbetween identical and precision aligned brass centering bell or bellchucks. Bell chuck centering is a purely mechanical method that relieson the fact that the lens will slide along the edge of the bell chuckuntil it seats itself at the zone of equal edge thickness. In thisalignment the optical axis of the lens and the mechanical axis of thespindle become colinear. When the edges of the centering chucks are wellrounded and polished, the lens surface will not be damaged, even at highchuck pressures. The bell chuck centering method with a horizontalspindle can be used for lenses with diameters as small as 3 mm and aslarge as 150 mm.

Still another centering method is bell chuck centering for largerlenses. Lenses up to 250 mm in diameter can be centered with this bellchucking method using vertically aligned spindles. For larger lenses, avacuum assist method is necessary to reduce the otherwise required highclamping loads on the lens surfaces that can lead to damage.

Regarding centerability limitations, for the centering method known astransfer spindle, there is no theoretical optical limit oncenterability, although some practical limits do exist. Even lenses withvery weak optical power can be centered with this method as long as thecentration error can be optically or mechanically detected. There is awell-defined centerability limit, however for the bell-chucking method.When the lens radii become too long, even strong forces will not preventthe lens from being displaced by the appreciable side pressures exertedby a side wheel typically formed of diamond. Before a lens productionrun is committed to a bell-chucking machine, it must first be determinedif the lens can be safely, accurately and reproducibly centered thisway.

The limit of centerability with the bell-chucking method is a functionof the slide angle of the lens relative to the chuck edge and thecoefficient of friction between lens and chuck. The motion componentwhich can be derived from chuck pressure causes the lens to move betweenthe bell chuck edges. This motion component must be large enough so thatit can overcome the friction between the bell chuck edges and the lenssurfaces. Since the value of this component depends on the shape of thelens, it is possible for it to become smaller than the frictioncomponent. The lens will then no longer slide between the bell chuckedges, and it can no longer be centered this way. The limit ofcenterability can be calculated from the lens diameter, the lens radii,and the coefficient of friction.

Doublet alignment is yet another prior art method based on aligning thedoublet to equal lens edge thickness. The doublet includes a convex anda concave lense joined together. The two lenses of a cemented or joineddoublet have a common optical axis.

For noncritical doublets it is sufficient to align the lenses by theircommon diameter. The doublet is put into a V-jig for this purpose. Thecemented doublet is then centered as accurately as individual lenses.The centering tolerances can be additive, however.

A somewhat more accurate centering method for doublets uses a fixture inwhich the doublet is held in a lens holder. Mounted above the doublet isa centering bell on the same axis as the lens holder. This centeringbell is lowered until it contacts the doublet, which will thenautomatically align the lense to an equal edge thickness. Alignment toequal edge thickness is also the principle on which an older instrumentwas based.

Doublets for high quality objectives are optically aligned. Atransmitted light method is well known for which the setup is equippedwith a collimator and a telescope. Systems are also used in which thelight from an autocollimator passes through a doublet and is reflectedback by a plane mirror.

Doublets can also be cemented and aligned to their common optical axison a laser centering test unit. The cement is applied and evenlydistributed. This method works best with UV cement. The lens pair isthen placed on the centering chuck of the instrument where it is held bylight vacuum pressure. The lower, typically concave, lens is pushedagainst a laterally attached V-stop which has been previously adjustedwith a centered lens and locked into position.

The laser passes through a focusing apparatus that compensates for therefractive powers of the doublet. A plane mirror redirects the beam fromthere through the doublet, which then passes through the hollow spindleand impinges as a light spot on a detector plate. The detector iselectronically coupled to an image screen that displays the light spotas a bright dot. A change in position of the light spot on the detectorplane is seen magnified many times on the image screen. The upper lensis then shifted in such a way that the dot on the screen remainsstationary as the spindle is rotated. The centered doublet is nowirradiated with UV light The cement sufficiently precures in a fewseconds, so then the cemented doublet can be removed from the centeringchuck and fully cured later in a ultra violet light oven.

The Laser Alignment and Assembly Station™ by Opto-Alignment Technology,Inc., is an instrument to improve quality of assembly and inspection ofprecision and ultra-precision multi-element lens assemblies. The LaserAlignment and Assembly Station™ operates by reflecting a laser beam fromany surface of an object being aligned or measured. A centering and tiltstage is mounted on an air bearing to bring the mechanical axis of alens housing into collinear alignment with the incident test beam. Theoptical module provides a focused laser test beam which, when reflectedfrom the surface under test, falls on a charge-coupled device (CCD)detector. If the surface is accurately centered, the reflection producesa stationary bright spot in the center of the video monitor. Amisaligned surface will reflect the laser beam at an angle and displacethe bright spot away from the center of the CCD. Rotation of the airbearing causes the decentered spot to orbit around the center of theCCD. The radius of the orbit viewed on a monitor is proportional to thetilt of the surface under test and is independent of its radius ofcurvature. A frame-grabber can be used to import the image to a computerand software can automate the measurements and store the data on theindividual lenses and the entire lens assembly.

Voice coil linear actuators with flexural bearings are also part ofprior art. The LFA-10 Linear Focus Actuator™ of Equipment Solutions Inc.is a positioning apparatus using such voice coil linear actuators. Itwas specifically developed for optical applications requiring both highprecision and high-speed positioning over a short to medium stroke. TheLFA-10 Linear Focus Actuator™ is well suited for optical focusing andother micropositioning applications such as scanning interferometry,surface structure analysis, disk drive testing, autofocus systems,confocal microscopy, biotechnology and semiconductor test equipment. TheLFA-10 Linear Focus Actuator™ is guided along a single axis by a flexuredesign. The use of flexures within the design produces a compact andlight package with zero stiction/friction, ultra-high resolution andexceptional guiding precision. This stage architecture allows it to beoriented in either a vertical or horizontal position. The LFA-10 LinearFocus Actuator™ uses a high force low mass moving voice coilarchitecture. The LFA-10 Linear Focus Actuator™ includes a sub-micronresolution linear displacement sensor.

All of the aforementioned methods are too slow to justify their capitalcost of equipment and operator labor. Note that executing a lensalignment method using automated pick and place machines is possible.However, such a method is not accurate enough due to imperfections inlens outlines and poor correlation between the outline of the lens andits optical axis.

SUMMARY OF THE INVENTION

What is needed is an improved apparatus having features for addressingthe problems mentioned above and new features not yet discussed. Broadlyspeaking, the present invention fills these needs by providing a methodof aligning the upper and lower centering bells of a lens doubletassembly machine. It should be appreciated that the present inventioncan be implemented in numerous ways, including as a method, a process,an apparatus, a system or a device. Inventive embodiments of the presentinvention are summarized below.

In one embodiment, a method of bell chuck aligning in a lens doubletaligning apparatus is provided. The method comprises positioning analignment tool with respect to a base plate of the lens doublet aligningapparatus. An upper bell shaft is positioned with respect to thealignment tool, wherein the upper bell shaft includes an upper bellchuck at a lower end of the upper bell shaft. Flexural bearings aretightened around an outer radial edge of the upper bell shaft, whereinthe flexural bearings precisely hold the upper bell shaft intoperpendicular alignment in the lens doublet aligning apparatus.

In another embodiment, a method of aligning a lower chuck with respectto an upper bell chuck of a lens doublet aligning apparatus is provided.The method comprises clamping a bell alignment ball between the upperbell chuck and the lower chuck. The lower chuck is translated radiallywith respect to the upper bell chuck. The lower chuck is aligned into acoaxial alignment position with the upper bell chuck. The lower chuck islocked into the coaxial alignment position.

In still another embodiment, an apparatus for aligning an upper bellchuck of a lens doublet aligning apparatus is provided. The apparatuscomprises an upper bell chuck. An upper bell shaft has the upper chuckattached at a lower end of the upper bell shaft. One or more flexuralbearings are included, wherein the one or more flexural bearings supportthe upper bell shaft in an upright position, such that the upper bellshaft traverses through a center of the one or more flexural bearings. Aflexural bearing housing is attached to outer radial edges of theflexural bearings, wherein the flexural bearing housing supports the oneor more flexural bearings within the flexural bearing housing. A baseplate supports a lower chuck and the flexural bearing housing on anupper portion of the base plate. An alignment tool shares coaxialalignment with the base plate.

In yet another embodiment, an apparatus for aligning a lower chuck withrespect to an upper bell chuck of a lens doublet aligning apparatus isprovided. The apparatus comprises an upper bell chuck. An upper bellshaft has the upper chuck attached at a lower end of the upper bellshaft. One or more flexural bearings, support the upper bell shaft in anupright position, wherein the upper bell shaft traverses through acenter of the one or more flexural bearings. A flexural bearing housingis attached to outer radial edges of the flexural bearings, wherein theflexural bearing housing supports the one or more flexural bearingswithin the flexural bearing housing. A base plate supports the lowerchuck and the flexural bearing housing on an upper portion of the baseplate. An alignment ball is clamped between the upper bell chuck and thelower chuck.

The invention encompasses other embodiments are configured as set forthabove and with other features and alternatives.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings. Tofacilitate this description, like reference numerals designate likestructural elements.

FIG. 1 shows an aligning method in which an upper lens is aligned withrespect to the top surface of a lower lens, in accordance with anembodiment of th present invention;

FIG. 2 shows an aligning method in which an upper lens is aligned withrespect to edge datums shared by the lower lens and a lower chuck, inaccordance with an embodiment of the present invention;

FIG. 3 is a perspective view of a lens aligning apparatus, in accordancewith an embodiment of the present invention;

FIG. 4 is a cut-away perspective view of the lens aligning apparatus ofFIG. 3, in accordance with an embodiment of the present invention;

FIG. 5 is close-up view of the flexural bearing of the lens aligningapparatus, in accordance with an embodiment of the present invention;

FIG. 6 shows the lens aligning apparatus during a lens aligning of theupper lens with respect to the upper bell chuck and the lower chuck, inaccordance with an embodiment of the present invention;

FIG. 7 shows the lens aligning apparatus during a lens raising of theupper lens in preparation for placement of the lower lens, in accordancewith an embodiment of the present invention;

FIG. 8 shows the lens aligning apparatus during a lens placement of thelower lens, in accordance with an embodiment of the present invention;

FIG. 9 shows the lens aligning apparatus during a lens aligning of theupper lens with respect to the lower lens, in accordance with anembodiment of the present invention;

FIG. 10 is an isometric cross-sectional view of the lens aligningapparatus during a bell alignment process of the upper bell chuck, inaccordance with an embodiment of the present invention;

FIG. 11 shows the lens aligning apparatus during a bell aligning of thelower chuck with respect to the upper bell chuck, in accordance with anembodiment of the present invention; and

FIG. 12 is a close-up view of the lens aligning apparatus during thebell aligning of FIG. 11, in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An invention for a method of aligning the upper and lower centeringbells of a lens doublet assembly machine is disclosed. Numerous specificdetails are set forth to provide a thorough understanding of the presentinvention. It will be understood, however, to one skilled in the art,that the present invention can be practiced with other specific details.Two different methods of lens doublet aligning are disclosed dependingon the centration requirements as shown in the diagrams below.

Overview of Lens Doublet Aligning

FIG. 1 shows an aligning apparatus 101 in which an upper lens L1 isaligned with respect to the top surface of a lower lens L2, inaccordance with an embodiment of the present invention. The lower lensL2 is preferably precisely held to be horizontal via edge datums 110shared between the lower lens L2 and a lockable lower chuck 104. Thechamfer 112 is a groove formed in the lockable lower chuck 104 byprecisely cutting the lockable lower chuck 104 such that the lockablelower chuck 104 meets the lower lens L2 at edge datums 110. Edge datums110 are precise edges shared between the lower lens L2 and the lockablelower chuck 104.

The lockable lower chuck 104 is allowed to translate radially in anydirection to allow the upper lens L1 to be seated in proper alignment ona raised ring 114 of the lower lens L2. The raised ring 114 is molded asa part of the lower lens L2. The raised ring 114 has a thickness ofbetween about 10 μm and about 15 μm. The raised ring 114 allows thelower lens L2 to behave as a lower bell. Accordingly, the raised ring114 serves as a lower bell contact and as a spacer to maintain a correctadhesive gap between the upper lens L1 and the lower lens L2. The raisedring 114 allows the upper lens L1 to self-align to the lower lens L2.Supporting precision balls 102 allow such radial and horizontaltranslation of the lockable lower chuck 104 in any direction. There areat least three supporting balls 102 to support the lockable lower chuck104. The precision balls 102 are surrounded by a thin layer of grease tohold the precision balls 102 in place during assembly and to reduce wearduring use. The upper bell chuck 108 precisely guides the upper lens L1into the proper position with respect to the top surface of the lowerlens L2.

FIG. 2 shows an aligning apparatus 201 in which an upper lens L1 isaligned with respect to the edge datums 110 shared by the lower lens L2and the lockable lower chuck 104, in accordance with an embodiment ofthe present invention. The lockable lower chuck 104 (or bottom fixture)is held fixed after alignment with respect to the upper bell chuck 108.Such an arrangement allows alignment 202 of the upper lens L1 withrespect to the edge datums 110.

The choice of techniques, between the apparatus of FIG. 1 and FIG. 2,depends on the desired optical characteristics of the doublet and thetolerances of various features on the lower lens L2. Note that lack ofsymmetry between the lenses is exaggerated in FIG. 1 and FIG. 2 tohighlight the differences in the two methods.

An important aspect of the present invention is the use of supportingprecision balls 102 to align the upper lens L1 with respect to the lowerlens L2. There are at least three supporting balls 102 to support thelockable lower chuck 104. In the apparatus of FIG. 1, the lenses areself-aligned by contact of their shared optical interfaces. Thisself-aligning is enabled by the radial freedom of the lockable lowerchuck 104. Another important aspect of the present invention is the useof supporting precision balls 102 to align the upper bell chuck 108 withrespect to the lockable lower chuck 104. The bell chuck aligning occursin an earlier step before the lens aligning. During the bell chuckaligning, the lockable lower chuck 104 is free to move radially withrespect to each other until locked in alignment by meltable wax or anyalternative method of attachment such as epoxy adhesive. However, beforethe lens aligning apparatus can be utilized to align the upper lens L1with respect to the lower lens L2, the upper bell chuck 108 needs to becalibrated or aligned with respect to the lockable lower chuck 104.

Details of Bell Chuck Aligning

FIG. 10 is an isometric cross-sectional view of the lens aligningapparatus during a perpendicularity aligning process 1001 of the upperbell chuck 108, in accordance with an embodiment of the presentinvention. The lens aligning apparatus is fitted with an alignment tool1003 for perpendicularity. The alignment tool 1003 ensuresperpendicularity of the upper bell chuck 108 with respect to the baseplate 304. A base plate bore 1007 positions the alignment tool 1003 withrespect to the base plate 304. The alignment tool 1003 includes athreaded hole 1005 for clamping the alignment tool 1003 with respect tothe base plate 304. A sleeve 1009 positions the upper bell shaft 406with respect to the alignment tool 1003 by contacting an outer radialedge of the upper bell shaft 406. The sleeve 1009 shares a coaxialcenter with the alignment tool 1003 and is supported in the alignmenttool 1003. After the upper bell shaft 406 is positioned into alignmentby the alignment tool 1003, the flexural bearings 308 are tightenedaround the outer radial edge of the upper bell shaft 406 using flexuralclamps 302. The flexural bearings 308 hold the upper bell shaft 406 suchthat the upper bell shaft 406 passes through a center axis of theflexural bearing housing 310 and the flexural bearings 308. The flexuralbearings 308 preferably precisely hold the upper bell shaft 406 intoperpendicular alignment and a centered position in the lens alignmentapparatus. The upper bell chuck 108 is part of a lower end of the upperbell shaft 406. The upper bell chuck 108 and the upper bell shaft 406share a coaxial axis. Accordingly, positioning the upper bell shaft 406automatically positions the upper bell chuck 108.

The alignment tool 1003 is bolted to the base plate 304 with a screwthrough the base plate bore 1007. The alignment tool 1003 comprises lowcoefficient of thermal expansion (CTE) material, preferably 6061-T6aluminum. The sleeve 1009 is comprises a higher CTE material, preferablyacetal. The upper bell shaft 406 is preferably 303 stainless steel. Thealignment tool 1003, the sleeve 1009, the base plate 304 and the upperbell chuck 108, including the upper bell shaft 406, are cooled in arefrigerator, preferably to approximately −20° C. The parts are thenremoved from the refrigerator. Before significant warming can occur, thealignment tool 1003 with attached base plate 304 is mated to the upperbell chuck 108 by inserting the upper bell chuck 108 into the alignmenttool 1003 to a depth that will result in the flexural bearings 308remaining planar during a subsequent step.

The combination alignment tool 1003 with base plate 304 is then allowedto warm to room temperature after which the remaining parts from thelens aligning apparatus are fitted to the combination. The flexuralbearings 308 are then clamped into alignment at their inner and outersurfaces by tightening a top nut 314 at the top of the upper bell shaft406 and the flexural clamp nuts 312 fastening the flexural clamps 302.

The entire lens aligning apparatus as shown in FIG. 10 is returned tothe refrigerator and cooled, preferably to approximately −20° C. Thelens aligning apparatus is then removed from the refrigerator. Thealignment tool 1003 is removed by unscrewing the screw holding thealignment tool 1003 to the base plate 304, detaching the base plate 304from the flexural bearing housing 310, and slipping the alignment tool1003 off the upper bell chuck 108. These steps, after removing the lensaligning apparatus from the refrigerator, are preferably carried outquickly while the cooled components are still cold.

Substantially all the parts shown in FIG. 10 are then allowed to warm toroom temperature before the base plate 304, without the alignment tool1003, is fastened to the flexure housing 310 with screws (not shown).The screws are set to a torque that matches that used during the roomtemperature flexure alignment, described above, to replicate any partdistortions that may have resulted from the attachment forces.

The axis of the upper bell chuck 108 is now perpendicular to the topsurface of the base plate 304. The perpendicularity is defined by theoutside shaft diameter, or outer radial edge, of the upper bell shaft406 with respect to a top surface of the base plate 304. The sleeve 1009is preferably machined with dimensions such that at room temperature thesleeve 1009 has a tight interference fit with the alignment tool 1003and the upper bell shaft 406. However, the machining should allow thesleeve 1009 to maintain an interference fit with the alignment tool 1003at approximately −20° C., but with a movable fit between the sleeve 1009and the upper bell shaft 406, thereby allowing insertion and removal ofthe alignment tool 1003. Such thermal properties of the componentsallows the upper bell chuck 108 to be held rigidly in perpendicularalignment with the base plate at the operating temperature, in otherwords, room temperature. The base plate bore 1007 with a stub (notshown) on the alignment tool 1003 ensures that all screw hole patternswill be in sufficient alignment to allow the flexure bearings 308 toalign to the upper bell shaft 406. The perpendicularity aligning process1001 is then complete.

FIG. 11 shows the lens aligning apparatus during a coaxial aligningprocess 1101 of the lockable lower chuck 104 with respect to the upperbell chuck 108, in accordance with an embodiment of the presentinvention. The upper bell is aligned to the lower bell by clamping abell alignment ball 1103 between the upper bell chuck 108 and lockablelower chuck 104 while allowing the lockable lower chuck 104 to translateradially. The lockable lower chuck 104 is initially free to translateradially. The lockable lower chuck 104 translates radially by rolling onits supporting precision balls 102 positioned between the lockable lowerchuck 104 and the base plate 304. There are preferably three supportingprecision balls 102 preferably evenly positioned at approximately 120degree spacing near the periphery of the lockable lower chuck 104 toallow radial translation. The clamping force is applied to the voicecoil actuator 306 of FIG. 3, thereby moving the upper bell chuck 108downward. The lockable lower chuck 104 is preferably locked into thealigned position by a curing epoxy 602. The curing epoxy 602 is alreadypre-applied between the underside of the lockable lower chuck 104 andthe pedestal just underneath the underside of the lockable lower chuck104. The curing epoxy 602 is also pre-applied to the supportingprecision balls 102. After the epoxy has cured, the clamping force andbell alignment ball 1103 are removed to complete the alignment processof the upper lens L1 and lower lens L2.

FIG. 12 is a close-up view 1201 of the lens aligning apparatus duringthe bell aligning 1101 of FIG. 11, in accordance with an embodiment ofthe present invention. The lockable lower chuck 104 is directly alignedwith the bell alignment ball 1103. The top of the surface of thelockable lower chuck 104 includes a chamfer 112. The lower surfaces ofthe lower lens L2 are the adjacent counterbore bottom and wall of thechamfer 112 of the lockable lower chuck 104. Accordingly, it isimportant that the chamfer of the lockable lower chuck 104 is accuratelymachined relative to the counterbore surfaces of the lower lens L2. Thecoaxial aligning process 1101 is then complete.

More Details of Lens Doublet Aligning

FIG. 3 is a perspective view 301 of a lens aligning apparatus, inaccordance with an embodiment of the present invention. The lensaligning apparatus includes, among other things, a base plate 304, anactuator 306, a flexural clamp 302, a flexural bearing 308, a flexurehousing 310, flexural clamp nuts 312, a top nut 314 and a floating lowerchuck 316. The flexural clamp 302 secures the flexural bearing 308 intoplace.

FIG. 4 is a cut-away perspective view 401 of the lens aligning apparatusof FIG. 3, in accordance with an embodiment of the present invention.The lens aligning apparatus further includes, among other things, theupper bell chuck 108, an upper bell shaft 406 and a vacuum passage 408.The upper bell chuck 408 is attached at a lower end of the upper bellshaft 406. One or more flexural bearings 308 support the upper bellshaft 406 in an upright position. The upper bell shaft 406 traversesthrough a center of the one or more flexural bearings 308. The flexuralbearing housing 310 is attached to outer radial edges of the flexuralbearings 308. The flexural bearing housing 310 supports the one or moreflexural bearings 308 within the flexural bearing housing. The baseplate 304 supports the lockable lower chuck 104 and the flexural bearinghousing on an upper portion of the base plate 304. A floating lowerchuck 316 is positioned to float above the lockable lower chuck 104 andthe base plate 304. The vacuum passage 408 passes traverses though acenter axis of the upper bell chuck 108. The base plate 304 supports themechanical insert 404, or heater 404, in a center portion of the baseplate 304. The heater 404 includes a drilled hole 402 for reducing heatconduction occurring from heat coils to the base plate 304.

FIG. 5 is a close-up view of the flexural bearing 308 of the lensaligning apparatus, in accordance with an embodiment of the presentinvention. Flexural bearings ensure highly repeatable linear translationof the upper bell chuck 108 with respect to lockable lower chuck 104.Additionally, stacks of flexural bearings 308 can be free to move toallow initial setup alignment and clamped to lock in the alignment.

FIG. 6 shows the lens aligning apparatus during an operation of lensaligning 601 of the upper lens L1 with respect to the upper bell chuck108 and the lockable lower chuck 104, in accordance with an embodimentof the present invention. The upper lens L1 is placed in the lockablelower chuck 104 by hand after the upper bell chuck 108 is preferablyraised approximately one quarter of inch (¼ in.) by a pneumatic cylinderof the upper bell chuck 108. Then, the upper bell chuck 108 is loweredfirst by the pneumatic cylinder and then by the voice coil 306. Theupper lens L1 is seated between the upper bell chuck 108 and thelockable lower chuck 104 by the force of the voice coil 306, and isthereby aligned with the bell chucks. A vacuum passage 408 is used forsubsequent handling of the upper lens L1. The floating lower chuck 316,discussed above with reference to FIG. 4, is optional. There are atleast three supporting balls 102 (two shown) to support the floatinglower chuck 316 above the base plate 304. As discussed above withreference go FIG. 1, there are at least three supporting balls 102 (twoshown) to support the lockable lower chuck 104 above the base plate 304.

FIG. 7 shows the lens aligning apparatus during a lens raising 701 ofthe upper lens L1 in preparation for placement of the lower lens L2, inaccordance with an embodiment of the present invention. The vacuumpassage 408 applies suction to the upper lens L1. Accordingly, the upperlens L1 is raised first by the voice coil 306, then by the pneumaticcylinder as the upper bell chuck 108 is raised.

FIG. 8 shows the lens aligning apparatus during a lens placing 801 ofthe lower lens L2, in accordance with an embodiment of the presentinvention. The lower lens L2 is precisely held to be horizontal via edgedatums 110 between the lower lens L2 and the lockable lower chuck 104.

FIG. 9 shows the lens aligning apparatus during a lens aligning 901 ofthe upper lens L2 with respect to the lower lens L2, in accordance withan embodiment of the present invention. The upper lens L1 is loweredonto the lower lens L2.

In the method of lens aligning according to FIG. 1, the lockable lowerchuck 104 is free to translate radially. Such radial freedom enhancesalignment of the upper lens L1 with respect to the lower lens L2, asdiscussed with reference to FIG. 1. The natural alignment of the opticalsurfaces of the upper lens L1 and the lower lens L2 is assured by anatural mating of the optical surfaces. When the ring on L2 is ofdiameter larger than a critical value to allow bell centering based onthe critical angle for friction. The natural mating of the opticalsurfaces occurs because the lockable lower chuck 104 is free totranslate radially. Accordingly, to some extent, the lens aligningapparatus relies on the ability of the lower lens L2 to self-align withthe upper lens L1 via the radial freedom of the lockable lower chuck104. This self-alignment of the lenses uses the upper surface of thelockable lower chuck 104 while perpendicular to the upper bell chuck108. This perpendicularity is accomplished during a previousperpendicularity aligning process 1001 of the upper bell chuck 108. Thisperpendicular aligning process 1001 is discussed above with reference toFIG. 10.

On the other hand, in the method of lens aligning according to FIG. 2,the lockable lower chuck 104 is fixed with respect to the upper bellchuck 108. In this embodiment, the upper bell chucks undergoes aprevious coaxial aligning process 1101 and is fixed into coaxialalignment. This coaxial aligning process 1101 is discussed above withreference to FIG. 11.

Once the lenses are aligned, the lenses are ultra-violet (UV) cured intoa doublet assembly. The upper bell chuck 108 is raised using thepneumatic cylinder. Then, the doublet assembly is removed by hand fromthe lens aligning apparatus.

Advantageously, the present invention is much lower in cost thanconventional methods when considering capital and operator labor. Areason for this costs savings is due to the passive aligning of thelower lens L2 to the upper lens L1. This passive aligning is enabled bya previous aligning of the upper bell chuck 108 and the lockable lowerchuck 104. The upper bell chuck 108 undergoes perpendicular bellaligning with respect to the lockable lower chuck 104, as discussed withreference to FIG. 10. The lockable lower chuck 104 undergoes coaxialbell aligning with respect to the upper bell chuck 108, as discussedwith reference to FIG. 11. The bell aligning utilizes, among otherthings, an alignment ball 1103, supporting precision balls 102 andcuring epoxy 602 to affix the lockable lower chuck 104 after aligningthe lockable lower chuck 104.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

1. A method of bell chuck aligning in a lens doublet aligning apparatus,the method comprising: positioning an alignment tool with respect to abase plate of the lens doublet aligning apparatus; positioning an upperbell shaft with respect to the alignment tool, wherein the upper bellshaft includes an upper bell chuck at a lower end of the upper bellshaft; and tightening flexural bearings around an outer radial edge ofthe upper bell shaft, wherein the flexural bearings precisely hold theupper bell shaft into perpendicular alignment in the lens doubletaligning apparatus.
 2. The method of claim 1, wherein the alignment toolcomprises of low coefficient of thermal expansion material.
 3. Themethod of claim 2, wherein the low coefficient of thermal expansionmaterial is acetal.
 4. The method of claim 1, wherein the upper bellshaft comprises of stainless steel.
 5. The method of claim 1, whereinthe positioning an upper bell shaft with respect to the alignment toolcomprises contacting the upper bell shaft with a sleeve, wherein thesleeve shares a coaxial center with the alignment and is support in thealignment tool.
 6. The method of claim 5, positioning an upper bellshaft with respect to the alignment tool comprises: cooling thealignment tool, the sleeve, the base plate, the upper bell shaft and theupper bell chuck; and mating the alignment tool and base plate to theupper bell chuck.
 7. The method of claim 6, wherein the alignment tool,the sleeve, the base plate, the upper bell shaft and the upper bellchuck are cooled to approximately −20 degrees C.
 8. The method of claim6, wherein positioning an upper bell shaft with respect to the alignmenttool further comprises warming the alignment tool, the sleeve, the baseplate, the upper bell shaft and the upper bell chuck to roomtemperature.
 9. The method of claim 8, wherein positioning an upper bellshaft with respect to the alignment tool further comprises: coolingagain the alignment tool, the sleeve, the base plate, the upper bellshaft and the upper bell chuck; and removing the alignment tool from thelens doublet aligning apparatus while the alignment tool, the sleeve,the base plate, the upper bell shaft and the upper bell chuck are stillcold.
 10. The method of claim 9, wherein removing the aligning tool fromthe lens doublet aligning apparatus comprises: unscrewing a screwholding the aligning tool to the base plate; detaching the base platefrom a flexural bearing housing; and slipping the alignment tool off theupper bell chuck.
 11. The method of claim 9, wherein the positioning anupper bell shaft with respect to the alignment tool further comprises:warming the base plate, the upper bell shaft and the upper bell chuck toroom temperature; and fastening the base plate, the upper bell shaft andthe upper bell chuck to the flexure housing.
 12. The method of claim 1,wherein the tightening the flexural bearings around an outer radial edgeof the upper bell shaft comprises clamping the flexural bearings intoalignment at inner and outer surfaces of the flexural bearings.
 13. Themethod of claim 12, wherein clamping the flexural bearings comprisestightening a top nut of the upper bell shaft and tightening flexuralclamp nuts.
 14. The method of claim 1, wherein perpendicular alignmentis defined by an outer radial edge of the upper bell shaft with respectto a top surface of the base plate.
 15. An apparatus for aligning anupper bell chuck of a lens doublet aligning apparatus, the apparatuscomprising: an upper bell chuck supported by an upper flexural bearing;an upper bell shaft having the upper chuck attached at a lower end ofthe upper bell shaft; one or more shaft flexural bearings, wherein theone or more shaft flexural bearings support the upper bell shaft in anupright position, wherein the upper bell shaft traverses through acenter of the one or more shaft flexural bearings; a flexural bearinghousing attached to outer radial edges of the shaft flexural bearings,wherein the shaft flexural bearing housing supports the one or moreshaft flexural bearings within the shaft flexural bearing housing; alower chuck supported by a lower flexural bearing; a base platesupporting the lower chuck and the shaft flexural bearing housing on anupper portion of the base plate; and an alignment tool sharing coaxialalignment with the base plate.
 16. An apparatus for aligning a lowerchuck with respect to an upper bell chuck of a lens doublet aligningapparatus, the apparatus comprising: an upper bell chuck supported by anupper flexural bearing; an upper bell shaft having the upper chuckattached at a lower end of the upper bell shaft; one or more shaftflexural bearings, wherein the one or more shaft flexural bearingssupport the upper bell shaft in an upright position, wherein the upperbell shaft traverses through a center of the one or more shaft flexuralbearings; a shaft flexural bearing housing attached to outer radialedges of the one of more shaft flexural bearings, wherein the shaftflexural bearing housing supports the one or more shaft flexuralbearings within the shaft flexural bearing housing; a lower chucksupported by a lower flexural bearing; a base plate supporting the lowerchuck and the shaft flexural bearing housing on an upper portion of thebase plate; and an alignment ball clamped between the upper bell chuckand the lower chuck.